Steam generation is necessary or desirable in many heavy oil recovery operations, including, for example, the recovery of tar sands from deposits in Northern Alberta, Canada, or elsewhere around the world. This is because in order to recover heavy oil from certain geologic formations, heating is required to increase the mobility of the oil to be recovered from the geologic formation. In order to produce steam for downhole use, water treatment plants are necessary to produce high quality water meeting the applicable specifications for a selected high pressure steam generator system. In most cases, the primary source of water to be treated in order to manufacture the required steam in the selected high pressure steam generator is de-oiled produced water, i.e. the water which is brought up along with the oil by production wells when oil is removed from the geologic formation. In such instances, oil must be separated from the produced water in order to provide a de-oiled produced water suitable for further treatment, prior to steam generation.
Various processes have been heretofore utilized or proposed for treatment of de-oiled produced waters. In those situations where the de-oiled produced waters contain relatively high levels of silica, the wastewater brines produced by the required water treatment plant inevitably contain high levels of silica. Silica is relatively soluble at high pH, however, high pH waters may, in some locales, be unsuitable for disposal by underground injection. The manufacture of wastewater brines for underground injection at neutral or near neutral pH would be desirable in order to eliminate the necessity to neutralize high pH wastewater brines, as well as the necessity to reduce or effectively eliminate from such wastewater brines the presence of silica above solubility limits before underground injection.
Thus, it can be appreciated that it would be advantageous to provide a produced water treatment process which minimizes the production of high pH wastewater brine streams, and that produces a neutral or near neutral pH wastewater brine suitable for underground injection.
The foregoing figures, being merely exemplary, contain various elements that may be present or omitted from actual process implementations depending upon the circumstances. An attempt has been made to draw the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the invention. However, various other elements of the unique process methods, and the combination of apparatus for carrying out the methods, are also shown and briefly described to enable the reader to understand how various features, including optional or alternate features or procedures, may be utilized in order to provide an efficient, cost effective process design which can be implemented in a desired throughput size and physical configuration for providing an optimum produced water treatment plant utilizing a calcium sulfate seeded crystallizing evaporator having an evaporator blowdown treatment system that produces a clear, effectively solids free treated brine suitable for downhole injection into a selected geologic formation.